(1) Field of the Invention
The present invention relates to a pressure-compensation device of a cartridge, and more particularly to a device that can be utilized to stabilize an internal backpressure of an ink bag inside the cartridge.
(2) Description of the Prior Art
In the computer industry, an ink jet printer, one of the well-known computer peripheral devices, performs printing jobs coordinated by the computer by providing ink drops from a cartridge through a print head onto a piece of paper or other recording media.
In the art, a well-designed cartridge for ink-jet printer should comply with the following two requirements:
1. While the cartridge is at an idle state, the internal pressure Pi of cartridge should be less than the external atmosphere pressure Po to prevent the cartridge from ink leakage through the print head.
2. While the cartridge is at a printing state, an additional pressure needs to be provided to increase the internal pressure Pi of the cartridge to overcome the external atmosphere pressure Po so that the ink inside the cartridge is able to drop out through the print head and accomplish the intended printing job.
To satisfy the aforesaid first requirement, a resort in the art is to add a backpressure Pb into the cartridge to provide a minus pressure for reducing the internal pressure Pi. By maintaining the internal pressure Pi of the cartridge to be less than the external atmosphere pressure Po during reservoir""s idle state, the possible ink leakage from the print head can be prevented.
On the other hand, to satisfy the aforesaid second requirement, a resolution in the art is to utilize a specific print head of thermal bubble type or piezoelectric pressure wave type, which is able to generate a proper print pressure P inside the cartridge during printing. When the printing pressure P is greater than the backpressure Pb, the internal pressure of cartridge Pi reaches a pressure level higher than the external atmosphere pressure Po so that the cartridge allows ink to drop out through the print head to perform the intended printing function. The art of print head is not within the scope of the present invention, therefore, no more efforts thereinafter will be devoted to it. The focus of the present invention is on stabilizing the internal backpressure Pb inside the cartridge to prevent the ink leakage or the fail of ink dropping problems.
Referring to FIG. 1 and FIG. 2, a conventional cartridge 10 with a pressure-compensation device 20 of U.S. Pat. No. 5,541,632 are shown respectively in an exploded view and a schematic application view. The cartridge 10 is a sealed rigid container that is constructed by an outer housing 11 and two outer covers 12, 13, and inside thereof further includes two resilient membranes 14, 15. A pressure-compensation device 20 and ink are installed inside the two resilience membranes 14, 15, where the pressure-compensation device 20 is used to maintain a proper backpressure Pb for keeping the internal pressure Pi to be less than the external atmosphere pressure Po to prevent from the ink leakage or the fail of ink dropping problems.
The pressure-compensation device 20 includes two inner covers 21, 22 and an arch spring 23, whereof outer centers of the inner covers 21, 22 are engaged respectively with the resilient membranes 14, 15, while their inner centers thereof are engaged with the arch spring 23.
Referring to FIG. 2, a free state of the arch spring 23 is presented in solid lines. As the ink inside the cartridge 10 gradually decreases along with the progression of printing operation, contractions from the two resilient membranes 14, 15 can move the inner covers 21, 22 inwards. At the same time, resilience of the arch spring 23 resists the inward movement of the inner covers 21, 22, so that the volume reduced by the two approaching resilient membranes 14, 15 is actually less than the volume loss caused by the running off of ink, by which a proper backpressure Pb can be provided inside the cartridge 10. In the art, it is the backpressure Pb that assures the proper ink supply during the printing operation and prevents the cartridge 10 from ink leaking through a print head thereof.
Nevertheless, the aforesaid pressure-compensation device 20 does exist some practical disadvantages. The major disadvantage is the stability control of the internal backpressure Pb inside the cartridge 10. Obviously, the internal backpressure Pb inside the cartridge 10 is correlated with the elastic coefficient of the arch spring 23. Yet, the aforesaid arch spring 23 is not a standardized spring, and theoretically the elastic coefficient of a perfect arch spring 23 for the cartridge 10 needs to vary along with the deformation of the spring 23 so as to provide a consistent forcing during the running off of the ink. Definitely, the arch spring 23 is not only difficult to be produced but also the varying elastic coefficient is hard to achieve. It is why instability of the backpressure usually happens to the conventional cartridge 10, which leads to possible ink leakage and failure to drop ink.
Accordingly, it is a primary object of the present invention to provide a pressure-compensation device of a cartridge for ink jet printers, which is able to adjust the backpressure inside the cartridge within a proper range to prevent the print head from the ink leakage or the fail of ink dropping problems.
The cartridge of the present invention is a sealed container with an air duct on the top and a print head on the bottom. The pressure-compensation device, located inside the cartridge, includes an ink bag, a tension spring, and a motion element.
The internal space of the ink bag is used to accommodate a substantial amount of ink for the print function of the print head. The ink bag, whose volume decreases along with the running off of ink, is made of a soft material. The tension spring, whose first end engages with the upper end of the ink bag and the second end engages with the motion element, is kept always at a tension state. As the ink inside the ink bag runs off along with the progression of printing operation, the volume of the ink bag also decreases. Simultaneously, the change of ink bag volume moves the tension spring and the motion element to maintain the tension spring at a tension state. The resilience of the tension spring restrains the contraction of the ink bag caused by the running off of ink so as to maintain a stable backpressure inside the ink bag, which prevents from the ink leakage or the fail of ink dropping problems through the print head of the cartridge.
The motion element of a first embodiment in accordance with the present invention is formed by a plurality of pulley sets, preferably by a pair of pulley sets. Each pulley set includes two fixed pulleys and a rope, whereof the two fixed pulleys are separately attached to the top and the bottom inside the cartridge, while the rope is connected with a second end of the tension spring and wound around the two fixed pulleys for rotation. A torque limiter could also be included at one fixed pulley of the two pulley sets, and therefore the fixed pulley must overcome the torque of the torque limiter in order to start rotating the pulley sets during the operation. The volume of the ink bag decreases along with the running off of ink. When the contraction force of the ink bag is greater than the torque of the torque limiter, the force can then move the tension spring and the rope simultaneously to keep the elongation of the tension spring within a proper range, and thereby a stable backpressure inside the cartridge can be induced to prevent from the ink leakage or the fail of ink dropping problems for the in jet printer.
The motion element of a second embodiment in accordance with the present invention is similar to a piston structure that includes a piston bar and a penetration hole from where the piston bar can extend to exterior of the cartridge. The piston bar is used to slide along inside the penetration hole whose internal surface can be farther coated or padded with a frictional material. When the volume of the ink bag decreases with the running off of ink and contraction of the ink bag is greater than the friction between the piston bar and the penetration hole, the ink bag moves the tension spring and the rope simultaneously to keep the deformation of the tension spring within a proper range, so that resilience of the tension spring can be induced to generate a stable backpressure inside the cartridge for preventing ink jet printers from the ink leakage or the fail of ink dropping problems.
The motion element of a third embodiment in accordance with the present invention is formed by a pulley set and a balancing weight. The pulley set includes two fixed pulleys and a rope, whereof two ends of the rope are connected respectively with the balancing weight and the ink bag. In this embodiment, the weight of the balancing weight becomes a drawing force acting upon the ink bag through the rope to restrain the contraction of the ink bag and to induce a required proper backpressure.
When the volume of the ink bag decreases with the running off of ink and the contraction force of the ink bag is greater than the weight of the balancing weight, the rope and the balancing weight can be moved simultaneously. In the present invention, it is noted that the force of the balancing weight acting upon the ink bag can be maintained steady at any stage, and thus the backpressure inside the ink bag is maintained at a stable state no matter how much ink remains in the ink bag. Up such an arrangement, the ink leakage or the fail of ink dropping problems can be avoided.